This invention relates to electronic device technology and the deposition of materials on portions of a microcircuit structure through openings in a separate mask.
The use of a separate mask to control the pattern of a material deposition on a portion of a structure is well known. Openings are provided in a sheet of mask material in a pattern which corresponds to the desired pattern of selected portions of the structure upon which material depositions are to be made. Then by use of such a mask in placing it against a structure surface and depositing on the selected portions through the mask openings, materials are deposited on the structure in approximately the desired geometrical arrangement. However, the final geometrical pattern of deposited material following this deposition differs from the desired geometrical pattern to some extent since, unavoidably, some of the material deposited gets underneath the mask along the edges of the openings therein during deposition. This occurs because the sheet of mask material is not uniformly in contact with the structure surface thereby leaving gaps between the mask and the structure surface. If these gaps occur, the method chosen of depositing material on the selected portions cannot be expected to alter greatly the result that some deposited material gets underneath the edges of the mask in a relatively uncontrolled manner.
Typical items upon which material depositions are desired to be made are integrated circuit wafers and substrates which are used to mount thereupon various kinds of electronic devices. The surfaces of these structures against which a mask is to be placed are usually very flat. This, in turn, requires that the mask be very flat against the surface if there is to be uniform contact and gaps are not to occur.
Such gaps can occur for flat sheet masks which are held by a holder which does not act to alter substantially the flat geometrical shape of the mask at portions of the mask intended to be brought against a surface of the structure. These gaps will occur when the structure surface and the mask are forced against one another, even though they are symmetrically aligned with one another and even though the mask and the structure surfaces are both flat and parallel, because of the bending of the mask due to the resultant forces acting on it due to the structures surface pressing against it and due to the mask holder constraining the edge of the mask. Failure of symmetrical and/or parallel alignment or deviations in flatness in the mask sheet itself, all difficult to avoid, are further sources of or aggrevations of such gaps. It is therefore desirable to have the mask and the structure surface placed in contact with one another in such a way as to minimize the formation of such gaps.